Treatment of thrombotic or atherosclerotic lesions in blood vessels using an endovascular approach has recently proven to be an effective and reliable alternative to surgical intervention in selected patients. For example, directional atherectomy and percutaneous translumenal coronary angioplasty (PTCA) with or without stent deployment are useful in treating patients with coronary occlusion. Atherectomy physically removes plaque by cutting, pulverizing, or shaving in atherosclerotic arteries using a catheter-deliverable endarterectomy device. Angioplasty enlarges the lumenal diameter of a stenotic vessel by exerting mechanical force on the vascular walls. In addition to using angioplasty, stenting, and/or atherectomy on the coronary vasculature, these endovascular techniques have also proven useful in treating other vascular lesions in, for example, carotid artery stenosis, peripheral arterial occlusive disease (especially the aorta, the iliac artery, and the femoral artery), renal artery stenosis caused by atherosclerosis or fibromuscular disease, superior vena cava syndrome, and occlusive iliac vein thrombosis resistant to thrombolysis.
It is well recognized that one of the complications associated with endovascular techniques is the dislodgment of embolic materials generated during manipulation of the vessel, thereby causing occlusion of the narrower vessels downstream and ischemia or infarct of the organ which the vessel supplies. In 1995, Waksman et al. disclosed that distal embolization is common after directional atherectomy in coronary arteries and saphenous vein grafts. See Waksman et al., American Heart Journal 129(3):430-5 (1995), incorporated herein by reference in its entirety. This study found that distal embolization occurs in 28% (31 out of 111) of the patients undergoing atherectomy. In January 1999, Jordan, Jr. et al. disclosed that treatment of carotid stenosis using percutaneous angioplasty with stenting is associated with more than eight times the rate of microemboli seen using carotid endarterectomy. See Jordan, Jr. et al., Cardiovascular surgery 7(1): 33-8 (1999), incorporated herein by reference in its entirety. Microemboli, as detected by transcranial Doppler monitoring in this study, have been shown to be a potential cause of stroke. The embolic materials include calcium, intimal debris, atheromatous plaque, thrombi, and/or air.
Filters mounted to the distal end of guidewires have been proposed for entrapment of vascular emboli. A majority of these devices includes a filter which is attached to a guidewire and is mechanically actuated via struts or a pre-shaped basket which deploys in the vessel. These filters are typically mesh “parachutes” which are attached to the shaft of the wire at the distal end, and to wire struts which extend outward in a radial direction at their proximal end. The radial struts open the proximal end of the filter to the wall of the vessel. Blood flowing through the vessel is forced through the mesh thereby capturing embolic material in the filter. These devices are self-directing and can be placed intravascularly.
However, there are several disadvantages associated with guidewire-filtration. First, the steerability of the guidewire may be altered as compared to conventional guidewires due to the size of the filter, and the guidewire may bend, kink, and/or loop around in the vessel, making insertion of the filter through a complex vascular lesion difficult. Secondly, the current filter designs, e.g., a basket or net, often fail to conform to the internal perimeter of the vessel, and distal embolization can still occur despite the filter placement. Thirdly, as the filter is stowed, the filter material is gathered together with “bunching” of the material at the perimeter, causing uncontrolled gathering and creating relatively large and poorly defined crossing profiles. As a result, the current filter designs require large capture sheaths to deploy and stow the filter.
What is needed are simple and safe blood filtering devices that conform to a patient's vessel wall to prevent distal embolization during endovascular procedures, and provide easy steerability and a controlled closure profile when contracted. Existing devices are inadequate for this purpose.